The use of seals formed from a rubber composition is made in many different sealing applications. In some such applications, the seal, for added stability and strength is formed from a rubber composition that has a metallic insert, such as a metal ring, embedded in the rubber.
In various railway brake apparatus, for example, fluid brake apparatus as described in U.S. Pat. No. 2,958,561, issued Nov. 1, 1960 to Harry C. May, and in U.S. Pat. No. 3,504,950, issued Apr. 7, 1970, to Glenn C. McClure, both of which were assigned to the assignee of the present invention, the use of rubber seals in the form of a ring are used, the seals having metallic inserts embedded therein. It is important that such ring seals have a size and strength within specific limits, and that such seals retain their predetermined configuration when in use so as to prevent leakage between the components between which the seals are positioned.
Such fluid brake apparatus for railway vehicles (as described in the above patents) have been designated in the industry as the 26 Brake Valve and has been in use for a period of time. At periodic intervals, namely within any twenty-four month period of operation, the brake valve is removed from the equipment and is completely dismantled, with various parts of the brake valve cleaned, inspected, lubricated, reassembled and tested. New rubber parts, such as seals, as specified in maintenance operation, are inserted at this time.
A prior process for forming a seal in the form of a rubber ring having a metallic insert embedded in the rubber ring used a compression molding technique. In the compression molding technique, a rubber batch was first mixed, calendared to a desired thickness and rubber rings punched out of the rubber composition. A compression mold was provided having a mold cavity base with upstanding spaced pins around a post in the mold cavity. A first punched rubber ring was disposed about the post on the pins and the metal insert was then disposed about the post and superimposed on the first punched rubber ring. A second punched rubber ring was then superimposed on the metal insert. The compression mold was then closed and the three piece unit was subjected to compression molding and curing to form the seal. The compression molding technique had problems in that the results were not readily reproducible and shifting or mis-alignment of the metal insert would occur during molding. For example, if one of the pins wore slightly more than others, a non-uniform thickness of rubber layer on one side of the metal insert relative to the other side could occur or a wavy or non-flat surface could result on the seal. It was often necessary to lap or smooth the top and/or bottom surface of a seal to a flat surface after compression molding. While such lapping provided a smooth flat surface, when the seal was used in a component a non-flat configuration of the top and/or bottom could result, which would result in a leaky seal. Often such a problem would not appear during examination of the seal but would appear only after the seal was put into use, cuasing other problems.